It has been common to treat a variety of medical conditions by introducing an insertable or implantable medical device such as stents, catheters or vena cava filters having a coating for release of a biologically active material into a body lumen of a patient. For example, various types of drug-coated stents have been used for localized delivery of drugs to a body lumen. See, e.g., U.S. Pat. No. 6,099,562 to Ding et al. Such coatings are generally manufactured by pre-mixing the drug with a dissolved polymer and using a spraying method or a dip coating method to deliver the mixture to the surface of the medical device. To spray the drug mixture, the drug must be well dispersed through a polymer coating mixture.
Also, because the drug or biologically active material can only tolerate a certain range of temperatures, the temperature at which the coating is dried or cured is restricted by the presence of the drug or biologically active material in the coating. More specifically, if the drug or biologically active material has a maximum temperature tolerance of 50° C., the polymer coating containing such drug or material should not be dried or cured above this temperature. Therefore, an application of a coating formulation that contains both a drug or biologically active material and polymer to a medical device can limit the temperature at which the coating is dried or cured and increase the amount of drying time required.
When a drug whose dosage must be strictly controlled is contained in the coating of such medical device, the amount of coating present on the medical device must be accurately adjusted. Previously, the only way to adjust the amount of coating on a medical device was to control the process parameters used to apply the coating composition onto the surface of the medical device to form the coating, such as controlling the application or spraying time and the flow rate of the coating solution. An improved method to manufacture a coated medical device having a strictly controlled amount of drug is needed.
In the conventional methods for coating medical devices, such as spray-coating or dipping, an entire surface or all surfaces of the medical device are coated even though it may be desired that only part of the surface is coated, or only some of the surfaces are coated. For instance, in medical devices having a tubular portion, such as a vascular stent, the inner surface of the tubular portion does not need to be coated with a coating containing a biologically active material that is used to treat only the body lumen wall that contacts the outer surface of the stent. When the entire outer surface of a medical device contains a biologically active material, this biologically active material can be delivered to both tissues in need of treatment, such as lesions and healthy body tissue.
Also, with existing coated medical devices, generally, the coating is uniformly applied along the entire length of the device or surface of the device. For example, conventional coated stents are coated uniformly along the entire length of their surface. By having the device uniformly coated along its length, the concentration release profile of the biologically active material along the length of the coated surface may be in the shape of a bell-curve, wherein the concentration of the biologically active material released at the middle of the surface is greater than the concentration of the biologically active material released at the ends of the coated surface.
Accordingly, there is a need for coated medical devices where the biologically active material can be positioned in predefined or selected regions of the medical device. Accordingly, there is a need for a method of applying a drug to the surface of a medical device. Also, there is a need for a method of making a coated medical device having a precise amount of a drug at predefined regions on the device and having a coating with a desired release profile.